Rise in violent crime not linked to mental illness

As seen in this story in the New Zealand Herald

The study, Myth and reality: the relationship between mental illness and homicide in New Zealand [Report Link Here], examined the files of 1501 murderers between 1970 and 2000. It found 133, or 8.9 per cent, were judged not fit to stand trial or not guilty by reason of insanity, in line with rates for low homicide countries internationally.

But an interesting trend emerged. Although the number of murders has tripled, from fewer than 20 a year in the early seventies to between 50 and 70 in recent years, the number of killings by the mentally ill has remained steady - and is usually less than six a year.

The study is one of only four in the world to look at time trends in homicides, and is touted to be the most comprehensive. Researchers satisfied ethical and privacy concerns to cross-match data from the police, coroners' office, Ministry of Health, Justice Department, Parole Board and New Zealand Herald archives.

So what explains the rise in violent crime?